Solar Concentration Systems (SCS) are used to increase the temperature of a working fluid by concentrating solar radiation thereon and making use of this heat energy, whether in industrial processes or in electrical power generation processes. Within the SCSs is found the central receiver tower systems, wherein solar radiation is concentrated by heliostats onto a receiver located at the top of a tower wherein it is transformed into thermal energy by the absorption of heat by the working fluid. An initial approach to central tower receiver technology according to patent U.S. Pat. No. 3,924,604 of 1974; the receiver described therein is the exterior type and has tubes arranged around the central axis of the tower, being located at the top of the tower, which in turn is located in the centre of a field of heliostats disposed in a circular manner. Subsequently, in 1983, a new configuration for a solar concentration tower plant was described by patent U.S. Pat. No. 4,400,946 wherein steam generation in a receptor disposed in a ring of a circular sector of the circumference described by the tower; other patents relating to this technology have been published since then seeking the optimisation of the different elements and processes of the system, such as U.S. Pat. No. 6,911,110 and WO2008118980, published in 2005 and 2008 respectively. One of the most important factors to be taken into account when a solar receiver is designed is heat losses. Heat losses in a solar concentration receiver tower are estimated at approximately 10%-20%, depending on the design. These losses may be of two kinds, heat losses by radiation and heat losses by convection. Furthermore, heat losses by radiation may be heat losses by reflection from the material and heat losses by emission from the material.
To increase the efficiency of solar concentration systems, different developments tend to be applied in the state serving to preheat the water which will circulate in the receiver.
Document WO 2009/044622 A1 describes a way to preheat the water by circulating it through tubes exposed to solar radiation before being sent to the receiver. Document WO 2008/154599 A1 also describes a way to preheat the water by passing it over electric preheaters which raise the temperature thereof before it enters the actual solar plant circuit.
Both solutions are examples of how to increase the efficiency of the system by preheating the water or heat transfer fluid before it circulates in the solar receiver, in order to obtain a higher temperature at the output of the receiver and, consequently, higher performance in the turbine and, therefore, greater system efficiency.
However, both developments use new energy to preheat the water. In the former case, the water is preheated with solar rays, which means a large area of land needs to be occupied by these tubes, as well as requiring the receptor not to be elevated. In the latter case, the water is preheated with an electric resistor, i.e., part of the energy which the plant produces is used to preheat the water, meaning that plant efficiency is penalised because of this self-consumption of electricity.
For all of these reasons, the object of the present invention is to provide a system for preheating the water before it enters the receiver which however differs from the known state of the art in that as preheating energy it uses the heat losses from the receiver itself, considerably increasing plant efficiency.